Hepatopreventive properties of hydroxytyrosol and mannitol-rich extracts obtained from exhausted olive pomace using green extraction methods

Exhausted olive pomace (EOP) is produced in olive-pomace oil extractors as a by-product. However, the obtention of bioactive compounds from EOP can reinsert it into the economy as a new bioresource before applying other exploitation ways. The objective of the present study was to investigate the phytochemical differences between aqueous and aqueous acetonic extracts from EOP (AE-EOP and AAE-EOP, respectively) obtained by hydrothermal and ultrasound-assisted extraction, respectively. The in vitro antioxidant activities and the in vivo hepatopreventive potential were evaluated. Using RP-HPLC-ESI-QTOF-MS, the chemical profile revealed that AE-EOP and AAE-EOP showed similar qualitative profiles, with some quantitative differences. Hydroxytyrosol and mannitol were the major compounds of the extracts. The investigation of antioxidant properties in vitro highlighted that AE-EOP was slightly more efficient in scavenging DPPH, ABTS, superoxide, and hydrogen peroxide radicals, when compared to AAE-EOP. Additionally, AE-EOP and AAE-EOP showed dose-dependent suppressive effects on pancreatic lipase activity. In vivo studies showed that AE-EOP and AAE-EOP presented interesting hepatopreventive capacities against CCl4 induced liver injury, as evidenced by (i) the preventive effects against DNA damage, (ii) the normalised hepatic biomarker parameters (ALT, AST, GGT, and LDH) and (iii) the normalised lipid profile (LDL-C, TC, TG, and HDL-C) through diminishing their levels, (iv) which was supported by Oil Red O analysis. Furthermore, AE-EOP and AAE-EOP reduced the oxidative stress in liver tissue by inhibiting lipid peroxidation together with the enhancement of the hepatic antioxidant activities (CAT, SOD and GPx) and GSH content. Additionally, AE-EOP and AAE-EOP exhibited an antifibrotic effect, which was clearly demonstrated by the histopathological examination using Picrosirius red staining. The obtained results support the use of EOP extracts in industries without further purification as antioxidants and against free radical induced damage.